The present invention relates to a printing apparatus, a driving condition setting method for a printhead, and a storage medium and, more particularly, to a printing apparatus including a printhead having a plurality of print elements and a driving means for generating pulse-like driving signals supplied to the printhead, a driving condition setting method for the printhead of the apparatus, and a storage medium.
Printing apparatuses such as a printer, copying machine, and facsimile are designed to print images made up of dot patterns on printing media (printing sheets) such as paper sheets and thin plastic sheets on the basis of image information.
The printing apparatuses can be classified into ink-jet printers, wire dot printers, thermal printers, laser beam printers, and the like according to the printing schemes. Recently, many printing apparatuses have been used and required to realize, for example, high-speed, high-resolution, high-image-quality, and low-noise printing.
As a printing apparatus that can meet such requirements, an ink-jet printing apparatus is available. This ink-jet printing apparatus is designed to discharge/eject ink (printing liquid) droplets from orifices of the printhead and make the droplets adhere to a printing medium, thereby printing images. This makes it possible to perform noncontact printing. Therefore, stable images can be formed on a variety of media.
Of such ink-jet printing apparatuses, a printer using a method of printing images by forming liquid droplets using heat energy has a simple structure, and hence allows nozzles to be easily arranged at a high density.
According to the operation principle of the ink-jet printing apparatus using heat energy, a pulse-like current is supplied to a heater, the ink is made to locally boil (foam) by the generated heat, and the ink is ejected from a nozzle by a shock wave produced by abrupt volume expansion at the time of evaporation of the ink.
Although this method allows a simple structure, since the heaters are in direct contact with ink, scorched ink adheres (kogation) to the heater surfaces, causing several problems. For example, uniformity on the heater surfaces is impaired, uniformity of foaming is also impaired, resulting in disturbance of the discharge direction (misdirection) and a decrease in heat conductivity with respect to the ink, which in turn cause a decrease in ink discharge amount (poor discharge) due to insufficient foaming. In general, to prevent this poor discharge, each heater is driven with a driving pulse width being set to necessary minimum +xcex1. If, however, the value of xe2x80x9c+xcex1xe2x80x9d is too large, the temperature of the heater rises too much, promoting kogation.
As methods of determining a proper driving pulse width, a method of ranking the resistance value of the heaters and a method of storing driving conditions in a printhead have been proposed.
In addition, as the density and number of nozzles increase, voltage variations due to changes in the number of nozzles driven at once cannot be neglected. In the past, driving pulses that allow sufficient ink discharge even at a drop in voltage were used. In this method, however, as the number of nozzles driven at once increases and a significant voltage drop occurs, excessive energy is applied to the heaters when the voltage does not drop too much. For this reason, a method of changing the pulse width depending on the magnitude of voltage drop has been proposed.
As described above, xe2x80x9cmisdirectionxe2x80x9d, xe2x80x9ckogationxe2x80x9d, and the like occur in the ink-jet printing apparatus unless proper driving conditions are set. Such faults become big factors that impair the durability of the printhead.
According to the conventional driving condition setting method, however, driving conditions are set in consideration of only conditions on the printhead side, and no consideration is given to variations and the like on the printer main body side. Furthermore, the driving conditions for the printhead change with time due to the influences of kogation and the like, but no consideration has been given to such secular changes.
It is the first object of the present invention to provide a printing apparatus which can easily set driving conditions in consideration of conditions on the printing apparatus main body side as well as at an arbitrary point of time.
It is the second object of the present invention to provide a driving condition setting method for a printhead which can easily set driving conditions in consideration of conditions on the printing apparatus main body side as well as at an arbitrary point of time, and a storage medium storing the method.
In order to achieve the first object, according to the present invention, there is provided a printing apparatus for performing printing on a printing medium by a printhead having a plurality of print elements, comprising driving means for generating a pulse-like driving signal supplied to the printhead, test pattern printing means for printing test patterns obtained by simultaneously driving a predetermined number of print elements of the plurality of print elements on the printing medium while a pulse width of the driving signal is decreased stepwise from a predetermined value, and control means for controlling a pulse width of a driving signal generated by the driving means on the basis of a boundary value of a pulse width with which a print element is not properly driven obtained from the test patterns.
In order to achieve the second object, according to the present invention, there is provided a driving condition setting method for a printhead in a printing apparatus including a printhead having a plurality of print elements and driving means for generating a pulse-like driving signal supplied to the printhead, comprising the test pattern printing step of printing test patterns obtained by simultaneously driving a predetermined number of print elements of the plurality of print elements on the printing medium while a pulse width of the driving signal is decreased stepwise from a predetermined value, and the control step of controlling a pulse width of a driving signal generated by the driving means on the basis of a boundary value of a pulse width with which a print element is not properly driven obtained from the test patterns.
The second object can also be achieved by a storage medium storing a program implementing the above method.
More specifically, according to the present invention, when driving conditions for a printhead are set in a printing apparatus including a printhead having a plurality of print elements and driving means for generating a pulse-like driving signal supplied to the printhead, test patterns obtained by simultaneously driving a predetermined number of print elements of the plurality of print elements are printed on the printing medium while the pulse width of the driving signal is decreased stepwise from a predetermined value, the boundary value of a pulse width with which a print element is not properly driven is obtained from the test patterns, and the pulse width of a driving signal generated by the driving means is controlled on the basis of the boundary value.
According to this method, driving conditions for the printhead can therefore be set at an arbitrary point of time in consideration of variations in conditions (power supply capacity and power line resistance) on the printer main body side as well as variations in conditions for the printhead (e.g., heater resistance, the ON resistance of each heater driving element, head wiring resistance, and heater thermal efficiency). This makes it possible to improve discharge stability and durability.
If the printhead includes a storage means for storing information about the characteristics of the print elements, a boundary value can be derived more quickly by making the test pattern printing means read out information from the storage means and determine a range in which the pulse width of the driving signal changes.
The control means preferably calculates the pulse width of a driving signal, from the boundary value, in a case where the number of print elements simultaneously driven differs from a predetermined number.
The test pattern printing means preferably prints a plurality of test patterns by changing the predetermined number.
The control means is preferably configured to calculate the pulse width of a driving signal by performing a predetermined computation for the boundary value.
The test pattern printing means preferably prints patterns while decreasing the amplitude of a driving signal at a predetermined rate, and the control means preferably controls the pulse width of a driving signal to the boundary value.
The test pattern printing means preferably includes storage means for storing information used to print test patterns.
The deriving means preferably includes a density sensor for detecting the density of a test pattern and obtains a boundary value from a change in detected density.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar throughout the figures thereof.